1. Field of the Invention
The present invention relates to an improvement in a continuously variable-speed drive such as a variable-speed drive of toroidal type used as a transmission of a motor vehicle and the like.
2. Related Background Art
A continuously variable-speed drive as shown in FIGS. 15 and 16 has been investigated such that it could be used as a transmission of a motor vehicle (for example, a motorcycle) having a relatively low engine output (for example, less than 100 HP), or as a transmission of a light vehicle running at a low speed, such as a lawn mower vehicle, snowplow vehicle, electric car, fork lift truck and the like, or as a transmission for rotating auxiliary equipment such as a compressor, generator and the like at an optimum speed regardless of the change in the number of revolutions of an engine thereof.
Such a variable-speed drive of toroidal type is generally designed so that an input disc 2 and an output disc 4 are attached to ends of an input shaft 1 and of an output shaft 3, respectively, and power rollers 6 each having an adjustable inclined angle are disposed between the input disc 2 and the output disc 4 (refer to the Japanese Utility Model Laid-Open No. 62-71465).
Inner surfaces 2a, 4a of the input and output discs 2, 4 which are opposed to each other have concave surfaces each having a toroidal profile, and a peripheral surface 6a of each power roller 6 has a spherical convex surface. The convex peripheral surfaces 6a of the power rollers 6 are abutted against the inner surfaces 2a, 4a of the discs. A pressurizing means 7 such as a loading cam is disposed between the input shaft 1 and the input disc 2, by which the input disc 2 is elastically biased toward the output disc 4.
In the case of the variable-speed drive of toroidal type having the arrangement as mentioned above, as shown in FIG. 15, when displacement shafts 5 of power rollers 6 are inclined so that the peripheral surfaces 6a of the power rollers 6 are abutted against the inner surface 2a of the input disc 2 near an innermost edge thereof and against the inner surface 4a of the output disc 4 near an outermost edge thereof, the reduction in speed can be provided between the input shaft 1 and the output shaft 3. To the contrary, when the displacement shafts 5 of the power rollers 6 are inclined so that the peripheral surfaces 6a of the power rollers 6 are abutted against the inner surface 2a of the input disc 2 near an outermost edge thereof and against the inner surface 4a of the output disc 4 near an innermost edge thereof as shown in FIG. 16, the increase in speed can be provided between the input shaft 1 and the output shaft 3. And, when the displacement shafts 5 are inclined to any condition between those shown in FIGS. 15 and 16, any intermediate speed ratio (between the maximum acceleration and deceleration) can be obtained between the input shaft 1 and the output shaft 3.
FIG. 17 shows a the variablespeed drive of toroidal type having the abovementioned arrangement and function incorporated into a transmission of a light car (more specifically, refer to the Japanese Patent Laid-Open No. 2-300549).
In this arrangement, a rotational drive force transmitted to a gear 8 via a power transmitting mechanism (not shown) and further to a power transmitting shaft 10 via a gear 9 meshed with the gear 8 is transmitted to the input shaft 1 of the variable-speed drive 12 via a clutch device 11. When the clutch device 11 is engaged, the rotational drive force of the power transmitting shaft 10 is transmitted to the output disc 4 via the input shaft 1, the pressurizing means of loading cam type (rollers 13 and cam plate 17), the input disc 2 and the power rollers 6 rotating around the displacement shafts 5. Further, the rotational drive force is outputted via a gear 15 fixedly mounted on an outer peripheral surface of a cylindrical portion 14 integrally formed on an outer surface 4b of the output disc 4 and serving as an output shaft of the transmission, and a gear 16 meshed with the gear 15.
Generally speaking, it is desirable that variable-speed drives such as the above-mentioned variable-speed drive the lightweight. However, in the above-mentioned variable-speed drive, since all of sectional configurations (taken along planes including axes of discs) of the input disc 2 and of the output disc 4 are the same (i.e., do not change in the circumferential direction), in order to ensure the adequate strength of the input and output discs 2,4, the thickness of each disc must be substantial. As a result, the disks are heavy and the construction could not be made as lightweight as would be desirable.